matchMedia.js

/*
* matchMedia() polyfill - test whether a CSS media type or media query applies
* primary author: Scott Jehl
* Copyright (c) 2010 Filament Group, Inc
* MIT license
* adapted by Paul Irish to use the matchMedia API
* http://dev.w3.org/csswg/cssom-view/#dom-window-matchmedia
* which webkit now supports: http://trac.webkit.org/changeset/72552
*
* Doesn't implement media.type as there's no way for crossbrowser property
* getters. instead of media.type == 'tv' just use media.matchMedium('tv')
*/

if ( !(window.matchMedia) ){
  
  window.matchMedia = (function(doc,undefined){
    
    var cache = {},
        docElem = doc.documentElement,
        fakeBody = doc.createElement('body'),
        testDiv = doc.createElement('div');
    
    testDiv.setAttribute('id','ejs-qtest');
    fakeBody.appendChild(testDiv);
    
    return function(q){
      if (cache[q] === undefined) {
        var styleBlock = doc.createElement('style'),
        	cssrule = '@media '+q+' { #ejs-qtest { position: absolute; } }';
        //must set type for IE!	
        styleBlock.type = "text/css";	
        if (styleBlock.styleSheet){ 
          styleBlock.styleSheet.cssText = cssrule;
        } 
        else {
          styleBlock.appendChild(doc.createTextNode(cssrule));
        } 
        docElem.insertBefore(fakeBody, docElem.firstChild);
        docElem.insertBefore(styleBlock, docElem.firstChild);
        cache[q] = ((window.getComputedStyle ? window.getComputedStyle(testDiv,null) : testDiv.currentStyle)['position'] == 'absolute');
        docElem.removeChild(fakeBody);
        docElem.removeChild(styleBlock);
      }
      return cache[q];
    };
    
  })(document);

}

Note: jdalton reported there may be an iphone incompat here https://gist.github.com/557891#gistcomment-21794

unconfirmed.

zakas has a similar script https://gist.github.com/08602e7d2ee448be834c

If I'm reading the documentation correctly, matchMedia() should return a MediaQueryList object rather than a Boolean, so this function really isn't a shim for the official one. Perhaps a name change would be useful to disambiguate?

Yeah agreed. I'd rather update this script to return a

{ matches: bool, media : mediaQueryStr } 

to make it a proper polyfill.

Over at https://gist.github.com/710855 I've fixed the return value, removed caching (caching isnt very responsive) and cleaned things up a bit.

I've also merged in Nicholas's work.

(I used the git interface so I was able to retain my gist # and this full git history. wooot)

And it's about time to move this from gists to a repo: https://github.com/paulirish/matchMedia.js :)